Glaze Ice Galore

2015-04-11 14:38:14.000 – Nate Iannuccillo, Summit Intern

 

It’s crazy to think that since I started interning in mid-January, I had yet to see temperatures above freezing on the summit until just yesterday, when we peaked at 44˚F in the afternoon. 

These temperatures brought about a slew of different weather phenomena as we transitioned through the freezing line. I found the abundance of glaze ice yesterday morning to be particularly interesting, so I figured I would talk about it a little bit.

So what is glaze ice?

Back in February, I explained the formation of rime ice, and discussed how water can exist in a supercooled state, which means that it stays as liquid water below 0˚C or 32˚F. The water forms rime ice when it freezes after coming into contact with a surface.

Going off of this basic definition, glaze ice is essentially the same thing as rime, but with some differences.

 To start, we’ll talk about the difference between freezing fog and freezing rain. Freezing fog leads to rime and freezing rain leads to glaze, so there’s a big connection here.

First, let’s take a look at the difference between a cloud droplet and a rain droplet. The cloud droplet exists as a liquid in a supercooled (below freezing yet still liquid) state whenever we experience freezing fog, and the rain droplet also exists in a supercooled state, except during a freezing rain event.

For our purposes, the primary difference between a rain droplet and a cloud droplet is the size. Rain droplets are much larger than cloud droplets. Take a look…

Raindrop size vs cloud droplet sizeImage Courtesy of Dr. Robert Houze, University of Washington Dept. of Atmospheric Sciences
 
 The smaller cloud droplets freeze more quickly than the much larger raindrops, and air gets trapped during the rapid freezing that occurs. This makes rime ice far less dense than glaze ice, and produces its white coloring. Conversely, glaze ice is relatively clear, and much denser and heavier than rime ice. This makes glaze much more dangerous when it accumulates on overhead objects.

With significant glaze accumulating yesterday morning, it felt quite necessary to wear a helmet going outside to de-ice with these heavy blocks of ice flying around.

Later last night, as we returned to sub-freezing temperatures, rime became the dominant form of ice once again.

Here’s a picture of a large chunk of glaze ice that I pulled off of the A-frame yesterday. You can see the contrast between glaze and rime quite well here. As the block of ice sat outside overnight, rime ice began to accumulate on top of the glaze ice. The color difference is quite noticeable. Check it out!

Rime and glaze ice

 

Nate Iannuccillo, Summit Intern

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